Moody's warning to George Osborne follows decision by Bank of England to halve growth forecast for 2013 to 1%

Moody's has warned the chancellor of the exchequer, George Osborne, that it will be carefully monitoring how he manages the difficult balancing act between growth and deficit reduction over the coming months. Photograph: Olivia Harris/Reuters

George Osborne was warned by one of the world's three biggest rating agencies on Wednesday night that the UK will lose its prized AAA credit status if the UK sinks into a triple-dip recession this winter.

In its annual health check on Britain, Moody's served notice to the chancellor that it would be carefully monitoring how he managed the difficult balancing act between growth and deficit reduction over the coming months.

The ratings firm said it had not yet decided whether to cut Britain's credit rating but said it could act in the new year either if growth prospects worsened or if Osborne failed to stick to a demanding timetable for reducing national debt.

The move came on the day that the Bank of England said the boost that accompanied the Olympics in the summer would be a one-off and halved its growth forecast for 2013 to 1%.

Moody's said: "The UK government's most significant policy challenge is balancing the need for fiscal consolidation against the need for economic stimulus."

The rating agency added that it would consider whether the UK should lose its AAA status in the new year once it had assessed how Osborne coped with its growth-deficit reduction dilemma in the Autumn Statement.

It said the coalition's attempts to reduce Britain's record peacetime budget deficit were being hampered by "weaker economic prospects as well as by the risks posed by the ongoing euro area sovereign debt crisis."

Moody's put the UK on negative watch – the threat of a downgrade in February this year.

It said last night three factors would govern its assessment: the likely speed of deficit reduction, the growth outlook and – most importantly – the likelihood that debt as a share of national income would not stabilise and start to come down over the next 3-4 years.

Speculation has been mounting in recent weeks that the independent Office for Budget Responsibility will force Osborne to admit in his autumn statement that slow growth will mean he can no longer meet his original aim of bringing down the debt to GDP ratio by 2015-16 without further austerity measures that would cut the economy's already sluggish growth rate.